- Sigma 10-20mm f3.5-4.5 has 102.4º-63.8º angle of view as per its website says
- Tokina 11-16 f2.8 has 104°~82° angle of view as per its website says
- Tamron 10-24mm f3.5-4.5 has 108°44' angle of view as per its website says

I believe these are diagonal angle of view right?

I am confuse to where I should look, the mm focal point or the angle of view... I want to choose the widest frame of any of the three can capture.

You need to check the small print and see what sensor size they are using for calculation. In this case, Sigma use their own sensor size which is slightly smaller than Nikon DX giving the apparently smaller FoV.